The present invention relates generally to transport temperature control systems and, more particularly, to transport temperature control systems having heating and cooling cycles which utilize hot compressor discharge gas.
Transportation temperature control systems typically can operate in either a cooling mode or a heating mode to provide the necessary conditions for a cargo container, such as a truck or trailer box section. Examples of such systems can be found in U.S. Pat. No. 4,419,866 to Howland; U.S. Pat. No. 4,748,818 to Satterness et al.; U.S. Pat. No. 4,912,933 to Renken; U.S. Pat. No. 5,056,324 to Haley; and U.S. Pat. No. 5,669,223 to Haley et al., all of which are incorporated herein by reference. Such systems switch between the cooling and heating modes of operation by way of a mode selector switch. In the cooling mode or cycle, hot compressor discharge gas is fed in series to a condenser, a receiver, a heat exchanger, an expansion valve, an evaporator, an accumulator and back to the compressor. In the heating mode or cycle, the mode selector diverts the hot compressor discharge gas to an evaporator defrost pan heater, the evaporator, the heat exchanger, the accumulator, and back to the compressor. The heating cycle is commonly used to defrost the evaporator. As generally known, in cold environments, such as during the winter months in cold climate areas, it is usually necessary for transportation temperature control systems to generate a certain amount of heat to keep the contents, typically food items or liquid drinks, contained within the truck or trailer box from freezing. Thus, the heating cycle can also be used to warm-up the truck or trailer box.
It is generally desirable to maximize the heating or defrosting capacity of the heating cycle in order to enhance the operation of a transport temperature control system. It has been observed that known transport temperature control systems sometimes fail to generate sufficient heat to ensure higher operating temperatures within a truck or trailer box when the box is subjected to a cold environment. It has also been observed that known transport temperature control systems sometimes lack enough heating capacity during a heating cycle to properly defrost the evaporator, which results in defrost timeouts because the evaporator does not reach a specified termination temperature during a specified time period. Thus, there is a need for a new and improved transport temperature control system having an increased heating capacity and a method of providing the same. In addition, there is a need to enhance the heating capacity of transport temperature control systems without significantly increasing the costs associated with such systems and without significantly increasing the overall size and weight of such systems so as not to adversely affect the operating efficiency of such systems.
The present invention provides a temperature control system having an increased heating performance. In one embodiment, the system includes a compressor adapted to compress a fluid, a heat exchanger coupled to the compressor such that compressed fluid moves from the compressor to the heat exchanger, and a pressure regulating valve positioned between the compressor and the heat exchanger such that compressed fluid from the compressor moves through the valve before reaching the heat exchanger. The pressure-regulating valve is designed to stay in a closed position until the pressure of the fluid from the compressor reaches a desired value. By virtue of this design, the pressure of the fluid is increased, thus resulting in an increase in the temperature of the fluid. Upon reaching the desired pressure, the valve opens to allow the highly-pressurized fluid to flow to the heat exchanger.
In one embodiment, the pressure-regulating valve includes a pressurized volume having a pressure charge sufficient to offset the compressor discharge pressure so as to close the pressure-regulating valve until such time as the desired compressor discharge pressure is reached. For example, the pressurized volume can be contained by a pressurized dome. In a preferred embodiment, the pressure regulating valve includes an upper plunger communicating with the pressurized volume, a lower plunger communicating with the pressurized fluid, and an actuating member (e.g., an actuating pin) coupling the upper plunger to the lower plunger.
The above-described system can be used in connection with a transport temperature control system that is capable of providing both heating and cooling. Such systems typically include an expansion valve fluidly coupled to the heat exchanger, a condenser fluidly coupled to the expansion valve, and a valve assembly (e.g., a three-way valve) fluidly coupled between the compressor and the pressure-regulating valve. The valve assembly can selectively direct pressurized fluid coming from the compressor to either the condenser (corresponding with the cooling mode) or the pressure regulating valve (corresponding with the heating mode). In the cooling mode, the heat exchanger acts as an evaporator.
The present invention is particularly suitable for increasing the heating performance of an existing temperature control system. To do this, the pressure-regulating valve is sold as a kit with a desired pressure charge. The valve is then installed in fluid communication between the valve assembly and the heat exchanger.